wire gap_filler into schedule engine, API, MCP

crates/api-types/src/channels.rs

@@ -35,6 +35,8 @@ pub struct UpdateChannelRequest {
     pub webhook_poll_interval_secs: Option<u32>,
     pub webhook_body_template: Option<Option<String>>,
     pub webhook_headers: Option<Option<String>>,
+    #[schema(value_type = Option<Option<Object>>)]
+    pub gap_filler: Option<Option<domain::MediaFilter>>,
 }
 
 #[derive(Debug, Clone, Serialize, Deserialize, ToSchema)]
@@ -55,6 +57,8 @@ pub struct ChannelResponse {
     pub webhook_poll_interval_secs: u32,
     pub webhook_body_template: Option<String>,
     pub webhook_headers: Option<String>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub gap_filler: Option<serde_json::Value>,
     pub created_at: DateTime<Utc>,
     pub updated_at: DateTime<Utc>,
 }
@@ -78,6 +82,7 @@ impl From<domain::Channel> for ChannelResponse {
             webhook_poll_interval_secs: c.webhook_poll_interval_secs(),
             webhook_body_template: c.webhook_body_template().map(|s| s.to_string()),
             webhook_headers: c.webhook_headers().map(|s| s.to_string()),
+            gap_filler: c.gap_filler().map(|f| serde_json::to_value(f).unwrap_or_default()),
             created_at: c.created_at(),
             updated_at: c.updated_at(),
         }

crates/application/src/channels/commands.rs

@@ -1,5 +1,5 @@
 use domain::models::ScheduleConfig;
-use domain::value_objects::{ChannelId, RotationPolicy, UserId};
+use domain::value_objects::{ChannelId, MediaFilter, RotationPolicy, UserId};
 
 pub struct CreateChannelCommand {
     pub owner_id: UserId,
@@ -16,6 +16,7 @@ pub struct UpdateChannelCommand {
     pub schedule_config: Option<ScheduleConfig>,
     pub rotation_policy: Option<RotationPolicy>,
     pub auto_schedule: Option<bool>,
+    pub gap_filler: Option<Option<MediaFilter>>,
 }
 
 pub struct DeleteChannelCommand {

crates/application/src/channels/tests/update.rs

@@ -45,6 +45,7 @@ async fn updates_channel_name() {
             schedule_config: None,
             rotation_policy: None,
             auto_schedule: None,
+            gap_filler: None,
         },
     )
     .await
@@ -82,6 +83,7 @@ async fn update_fails_if_not_owner() {
             schedule_config: None,
             rotation_policy: None,
             auto_schedule: None,
+            gap_filler: None,
         },
     )
     .await;
@@ -108,6 +110,7 @@ async fn update_nonexistent_channel_returns_not_found() {
             schedule_config: None,
             rotation_policy: None,
             auto_schedule: None,
+            gap_filler: None,
         },
     )
     .await;
@@ -148,6 +151,7 @@ async fn update_config_creates_snapshot() {
             schedule_config: Some(new_config),
             rotation_policy: None,
             auto_schedule: None,
+            gap_filler: None,
         },
     )
     .await
@@ -187,6 +191,7 @@ async fn update_without_config_skips_snapshot() {
             schedule_config: None,
             rotation_policy: None,
             auto_schedule: None,
+            gap_filler: None,
         },
     )
     .await
@@ -225,6 +230,7 @@ async fn update_description_clear() {
             schedule_config: None,
             rotation_policy: None,
             auto_schedule: None,
+            gap_filler: None,
         },
     )
     .await
@@ -243,6 +249,7 @@ async fn update_description_clear() {
             schedule_config: None,
             rotation_policy: None,
             auto_schedule: None,
+            gap_filler: None,
         },
     )
     .await

crates/application/src/channels/update.rs

@@ -35,6 +35,9 @@ pub async fn execute(deps: &ChannelCommandDeps, cmd: UpdateChannelCommand) -> Do
     if let Some(auto) = cmd.auto_schedule {
         channel.set_auto_schedule(auto);
     }
+    if let Some(gap_filler) = cmd.gap_filler {
+        channel.set_gap_filler(gap_filler);
+    }
 
     deps.channel_command.save(&channel).await?;
 

crates/domain/src/services/schedule/mod.rs

@@ -9,7 +9,8 @@ use crate::models::{
     ScheduledSlot,
 };
 use crate::ports::{ChannelQuery, LibraryQuery, ScheduleCommand, ScheduleQuery};
-use crate::value_objects::{BlockId, ChannelId, FillStrategy, InterstitialRule, LibrarySearchFilter, MediaItemId, MediaRole, RotationPolicy, Weekday};
+use crate::models::MediaItem;
+use crate::value_objects::{BlockId, ChannelId, FillStrategy, InterstitialRule, LibrarySearchFilter, MediaFilter, MediaItemId, MediaRole, RotationPolicy, Weekday};
 
 mod fill;
 mod rotation;
@@ -153,6 +154,13 @@ impl ScheduleEngineService {
 
         slots.sort_by_key(|s| s.start_at());
 
+        if let Some(gap_filter) = channel.gap_filler() {
+            let filler_items = self.query_gap_fillers(gap_filter).await?;
+            if !filler_items.is_empty() {
+                Self::fill_gaps(&mut slots, &filler_items, valid_from, valid_until);
+            }
+        }
+
         let schedule = GeneratedSchedule::new(
             channel_id,
             valid_from,
@@ -415,6 +423,71 @@ impl ScheduleEngineService {
 
         Ok(slots)
     }
+
+    async fn query_gap_fillers(&self, gap_filter: &MediaFilter) -> DomainResult<Vec<MediaItem>> {
+        let filter =
+            media_filter_to_library_search(gap_filter).with_role(MediaRole::Interstitial);
+        let (items, _) = self.library_query.search(&filter).await?;
+        Ok(items)
+    }
+
+    fn fill_gaps(
+        slots: &mut Vec<ScheduledSlot>,
+        fillers: &[MediaItem],
+        valid_from: DateTime<Utc>,
+        valid_until: DateTime<Utc>,
+    ) {
+        if fillers.is_empty() {
+            return;
+        }
+
+        let gap_block_id = BlockId::generate();
+        let mut gap_slots: Vec<ScheduledSlot> = Vec::new();
+        let mut filler_idx = 0usize;
+
+        let mut boundaries: Vec<(DateTime<Utc>, DateTime<Utc>)> = Vec::new();
+
+        if slots.is_empty() {
+            boundaries.push((valid_from, valid_until));
+        } else {
+            if slots[0].start_at() > valid_from {
+                boundaries.push((valid_from, slots[0].start_at()));
+            }
+            for pair in slots.windows(2) {
+                if pair[1].start_at() > pair[0].end_at() {
+                    boundaries.push((pair[0].end_at(), pair[1].start_at()));
+                }
+            }
+            if let Some(last) = slots.last() {
+                if last.end_at() < valid_until {
+                    boundaries.push((last.end_at(), valid_until));
+                }
+            }
+        }
+
+        for (gap_start, gap_end) in boundaries {
+            let mut cursor = gap_start;
+            while cursor < gap_end {
+                let filler = &fillers[filler_idx % fillers.len()];
+                let filler_end =
+                    (cursor + Duration::seconds(filler.duration_secs() as i64)).min(gap_end);
+                if filler_end <= cursor {
+                    break;
+                }
+                gap_slots.push(ScheduledSlot::new(
+                    cursor,
+                    filler_end,
+                    filler.clone(),
+                    gap_block_id,
+                ));
+                cursor = filler_end;
+                filler_idx += 1;
+            }
+        }
+
+        slots.append(&mut gap_slots);
+        slots.sort_by_key(|s| s.start_at());
+    }
 }
 
 fn media_filter_to_library_search(filter: &crate::value_objects::MediaFilter) -> LibrarySearchFilter {

crates/domain/src/services/schedule/tests/integration.rs

@@ -420,3 +420,138 @@ async fn interstitial_min_gap_respected() {
         "no interstitials should be inserted when programs are shorter than min_gap_secs"
     );
 }
+
+impl TestHarness {
+    async fn create_channel_with_blocks_and_gap_filler(
+        &self,
+        blocks: Vec<ProgrammingBlock>,
+        gap_filler: Option<MediaFilter>,
+    ) -> Channel {
+        let mut channel = Channel::new(
+            crate::value_objects::UserId::generate(),
+            "test-channel",
+            "UTC",
+        );
+        let today = Utc::now()
+            .with_timezone(&chrono_tz::UTC)
+            .date_naive();
+        let weekday = Weekday::from(today.weekday());
+        let mut config = ScheduleConfig::new();
+        config.insert_day(weekday, blocks);
+        channel.set_schedule_config(config);
+        channel.set_gap_filler(gap_filler);
+        self.channel_repo
+            .channels
+            .lock()
+            .unwrap()
+            .insert(channel.id(), channel.clone());
+        channel
+    }
+}
+
+#[tokio::test]
+async fn gap_filler_fills_between_blocks() {
+    let h = TestHarness::new();
+    h.seed_items(vec![
+        movie("prog1", 1800),
+        movie("prog2", 1800),
+        interstitial("filler1", 60),
+        interstitial("filler2", 60),
+    ]);
+
+    let block1 = ProgrammingBlock::new_algorithmic(
+        "morning",
+        NaiveTime::from_hms_opt(8, 0, 0).unwrap(),
+        30,
+        MediaFilter::default(),
+        FillStrategy::BestFit,
+    );
+    let block2 = ProgrammingBlock::new_algorithmic(
+        "afternoon",
+        NaiveTime::from_hms_opt(10, 0, 0).unwrap(),
+        30,
+        MediaFilter::default(),
+        FillStrategy::BestFit,
+    );
+
+    let channel = h
+        .create_channel_with_blocks_and_gap_filler(
+            vec![block1, block2],
+            Some(MediaFilter::default()),
+        )
+        .await;
+
+    let schedule = h
+        .engine
+        .generate_schedule(channel.id(), Utc::now())
+        .await
+        .unwrap();
+
+    let filler_count = schedule
+        .slots()
+        .iter()
+        .filter(|s| *s.item().role() == MediaRole::Interstitial)
+        .count();
+
+    assert!(
+        filler_count > 0,
+        "gap filler should produce interstitial slots between blocks"
+    );
+
+    for pair in schedule.slots().windows(2) {
+        assert!(
+            pair[0].end_at() <= pair[1].start_at(),
+            "slots overlap: {} ends at {:?} but {} starts at {:?}",
+            pair[0].item().title(),
+            pair[0].end_at(),
+            pair[1].item().title(),
+            pair[1].start_at(),
+        );
+    }
+}
+
+#[tokio::test]
+async fn no_gap_filler_leaves_gaps_empty() {
+    let h = TestHarness::new();
+    h.seed_items(vec![
+        movie("prog1", 1800),
+        movie("prog2", 1800),
+        interstitial("filler1", 60),
+    ]);
+
+    let block1 = ProgrammingBlock::new_algorithmic(
+        "morning",
+        NaiveTime::from_hms_opt(8, 0, 0).unwrap(),
+        30,
+        MediaFilter::default(),
+        FillStrategy::BestFit,
+    );
+    let block2 = ProgrammingBlock::new_algorithmic(
+        "afternoon",
+        NaiveTime::from_hms_opt(10, 0, 0).unwrap(),
+        30,
+        MediaFilter::default(),
+        FillStrategy::BestFit,
+    );
+
+    let channel = h
+        .create_channel_with_blocks_and_gap_filler(vec![block1, block2], None)
+        .await;
+
+    let schedule = h
+        .engine
+        .generate_schedule(channel.id(), Utc::now())
+        .await
+        .unwrap();
+
+    let filler_count = schedule
+        .slots()
+        .iter()
+        .filter(|s| *s.item().role() == MediaRole::Interstitial)
+        .count();
+
+    assert_eq!(
+        filler_count, 0,
+        "no gap filler configured, should have no interstitial slots"
+    );
+}

crates/mcp/src/server.rs

@@ -47,6 +47,7 @@ pub struct UpdateChannelParams {
     pub timezone: Option<String>,
     pub description: Option<String>,
     pub schedule_config_json: Option<String>,
+    pub gap_filler_json: Option<String>,
 }
 
 #[derive(Debug, Deserialize, JsonSchema)]
@@ -98,7 +99,7 @@ impl KTvMcpServer {
         channels::create_channel(&self.channel_cmd_deps, self.owner_id, &p.name, &p.timezone).await
     }
 
-    #[tool(description = "Update channel name, timezone, description, and/or schedule config")]
+    #[tool(description = "Update channel name, timezone, description, schedule config, and/or gap_filler")]
     async fn update_channel(&self, #[tool(aggr)] p: UpdateChannelParams) -> String {
         let id = match parse_uuid(&p.id) {
             Ok(id) => id,
@@ -114,6 +115,17 @@ impl KTvMcpServer {
             },
             None => None,
         };
+        let gap_filler = match p.gap_filler_json {
+            Some(json) if json == "null" => Some(None),
+            Some(json) => match serde_json::from_str(&json) {
+                Ok(f) => Some(Some(f)),
+                Err(e) => {
+                    return serde_json::json!({"error": format!("invalid gap_filler_json: {e}")})
+                        .to_string()
+                }
+            },
+            None => None,
+        };
         channels::update_channel(
             &self.channel_cmd_deps,
             id,
@@ -122,6 +134,7 @@ impl KTvMcpServer {
             p.timezone,
             p.description,
             schedule_config,
+            gap_filler,
         )
         .await
     }

crates/mcp/src/tools/channels.rs

@@ -53,6 +53,7 @@ pub async fn update_channel(
     timezone: Option<String>,
     description: Option<String>,
     schedule_config: Option<domain::ScheduleConfig>,
+    gap_filler: Option<Option<domain::MediaFilter>>,
 ) -> String {
     let cmd = UpdateChannelCommand {
         channel_id: channel_id.into(),
@@ -63,6 +64,7 @@ pub async fn update_channel(
         schedule_config,
         rotation_policy: None,
         auto_schedule: None,
+        gap_filler,
     };
     match application::channels::update::execute(cmd_deps, cmd).await {
         Ok(channel) => ok_json(&channel),

crates/presentation/src/handlers/channels.rs

@@ -71,6 +71,7 @@ pub async fn update_channel(
         schedule_config: req.schedule_config.map(Into::into),
         rotation_policy: req.rotation_policy,
         auto_schedule: req.auto_schedule,
+        gap_filler: req.gap_filler,
     };
     let channel = application::channels::update::execute(&state.channel_command_deps, cmd).await?;
     Ok(Json(ChannelResponse::from(channel)))